THE RELAXATION OF B STATE MOLECULAR IODINE ADSORBED ON NONMETALLIC SOLID SURFACES

KEITH RICHARD EVANS, Purdue University

Abstract

It was shown that the use of visible laser spectroscopy in the attentuated total reflectance mode coupled with the phenomena of total internal reflection can be a useful tool for the characterization of the visible absorption spectrum of adsorbed molecules on nonmetallic surfaces. This technique showed that the visible absorption spectra of iodine adsorbed from the gas phase onto various nonmetallic solid surfaces strongly resembles the absorption spectra of related iodine complexes in solution and in the gas phase. Measurement of the absorption spectrum of iodine adsorbed on a LiF solid surface as a function of iodine pressure and at two different temperatures led to the determination of the enthalpy of binding of I(,2) to the surface. The value of the binding or adsorption enthalpy was found to be slightly higher than the approximate value that is expected when only van der Waal's forces are operating, indicating that partial charge transfer is involved in the binding. It was experimentally ascertained that the predominant mode of relaxation of the laser excited adsorbed iodine molecule was a nonradiative mechanism; the use of simple modeling and extrapolation of theory developed for gas phase iodine complexes led to the conclusion that the operating mechanism was surface-catalyzed electronic predissociation of the iodine intermolecular bond. Auxiliary experiments suggested that the fate of the iodine atoms that resulted from the predissociation of I(,2) on the surface was an eventual recombination on the surface, followed by rapid vibrational energy transfer to the surface (phonon modes), with desorption occurring at a later time.

Degree

Ph.D.

Subject Area

Chemistry

COinS